Site Results

Site 1053 is located at the top of an escarpment cut into the upper part of Blake Nose. The location of Site 1053 was chosen to recover middle Eocene to upper Eocene deposits and extend the depth transect into water depths (~1652 mbsl) equivalent to the depth of modern intermediate waters. The MCS seismic profile Line TD-5 suggests that the middle Eocene interval is about as expanded at Site 1053 as it is at Site 1051. Reflectors in the MCS line indicate that a substantial thickness of upper Eocene and younger sediments not found at deeper sites is present at Site 1052. The upper Eocene section is expected to contain a high temporal resolution record of ocean structure, magnetic reversals, and biological evolution, particularly during times of rapid climate change like the late Eocene-Oligocene onset of glaciation and the early to middle Eocene cooling. The lithologic cycles should provide a high quality cyclostratigraphy to enhance both the magnetochronology and biochronologies, as well as improve correlation between sites in the depth transect. The primary reason for drilling this site was to extend the depth transect up the slope of Blake Nose for studies of Eocene deep-water structure. An additional goal was to recover sediments belonging to the upper Eocene and possibly the Eocene/Oligocene boundary that could be used to describe the timing of the onset of Antarctic glaciation and debris from upper Eocene tektite strewn fields.

Site 1053 recovered an exceptionally thick upper Eocene section consisting mainly of siliceous nannofossil ooze. This thick section might reflect periods of increased productivity in the surface waters or enhanced preservation on the seafloor.

The top of the cored interval is a 5- to 37-cm-thick layer with manganese nodules and a drilling slurry of clayey foraminifer ooze that is rich in phosphatic debris, including fish scales and vertebrae. Below this is ~12.5 m of pale yellow upper Eocene siliceous nannofossil ooze with varying amounts of foraminifers and clay. As at Sites 1050, 1051, and 1052, there is a sharp color change from pale yellow to light greenish gray. This sharp color change is time-transgressive across the four sites, and there is no discernible compositional difference in the sediment across this boundary. Green siliceous nannofossil ooze is ~126 m thick in Hole 1053A and ~114 m thick in Hole 1053B. Several ash layers are present, including a distinctive 8-cm-thick, highly altered, clay- and diatom-rich layer. At least 20 species of diatoms are present in this layer, whereas diatoms are not abundant or diverse elsewhere at Site 1053. Preservation of diatoms in this layer may have been enhanced due to leaching of silica during ash alteration. The lowermost 50 m of cored section consists of middle Eocene greenish gray chalk with varying amounts of nannofossils, siliceous microfossils, and clay. Drilling disturbance has resulted in slight to heavy biscuiting in the core.

Light/dark color alternations within the greenish sediment are often visible, with the darker intervals being more clay-rich. Correlating the two holes, however, by using magnetic susceptibility and GRAPE density data from the MST track and the Minolta color spectrophotometer proved to be difficult, as the signals were noisy mainly because of significant bioturbation. Nevertheless, the shipboard composite section shows that most likely a complete record was recovered.

Shipboard paleomagnetic results were not straightforward and need to be improved by post-cruise analysis of discrete samples. However, a detailed biostratigraphy was obtained by integration of nannofossil, planktonic foraminifer, and radiolarian datum levels. The radiolarians in particular appear to be very useful at this site. We expected to find evidence for upper Eocene meteor impacts near two well-defined extinction levels of radiolarians in the upper Eocene. The extinction levels were found, but tektites were not visible in the sediment, probably due to extensive bioturbation. We are hopeful that shore-based research will detect the tektites and other evidence for impact debris. Detailed biochronological control and excellent preservation of the calcareous microfossils make this site suitable for meeting our paleoceanographic objectives.

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